2 layers of 50mm celotex board v 1 layer of 100mm

SG27

As silly as this sounds would it make any difference using 2 layers of 50mm v 1 layer of 100mm? Would the thermal properties be roughly the same? It will be to insulate a stud wall which boarders a cold roof void.

The reason for not using 100mm to start with is I will need to slide the boards up behind a beam and it would be much easier with thinner boards. Also I can only get the 100mm boards in 2400x1200 which I would need to chop up so I could fit it in the car! The 50mm comes in handy small boards which are much more convenient for the gaps I need to fit them in.

Any thoughts?

troffasky

Look at the u-values of the two products on the spec sheets, that's where the answer will be.

You might have something to gain by using two layers - you can offset them so you never joins in both layers, in the same place.

that

the celotx will drop in R value over 7-15 years, and become equivalent R-value of polystyrene

stator

The R-value of celotex seems to double between 50mm and 100mm, so yes it would seem to be equivalent.


Product Code Thickness (mm) R-value (m²K/W) Weight (kg/m²)
GA4050 50 2.25 1.55
GA4055 55 2.50 1.70
GA4060 60 2.70 1.88
GA4065 65 2.95 2.03
GA4070 70 3.15 2.17
GA4075 75 3.40 2.32
GA4080 80 3.60 2.46
GA4090 90 4.05 2.74
GA4100 100 4.50 3.28

kr147

This is good timing as I was wondering something similar to this myself!

Gloomendoom

stator wrote: »

The R-value of celotex seems to double between 50mm and 100mm, so yes it would seem to be equivalent.

I would have assumed so although, if there is a gap between the faces of the two sheets, air movement may reduce the effectiveness.

FreeBear

SG27 wrote: »

Also I can only get the 100mm boards in 2400x1200 which I would need to chop up so I could fit it in the car!

Standard size for both 50mm and 100mm sheets is 2400x1200 - Depending on quantity needed, order from a builders merchant and bug them for free delivery. I regularly do this when I need materials for a job, and I also haggle over the price and certainly match the price of the DIY stores on most things.

SG27

Gloomendoom wrote: »

I would have assumed so although, if there is a gap between the faces of the two sheets, air movement may reduce the effectiveness.

Yes this is what I was thinking, even the foil against foil might make a difference. But to be honest for the difficulty it would cause to use the 100mm im not too fussed!